This invention relates to a suspension system for an automobile and, in particular, to a system for changing the damping force of shock absorbers of the suspension system or the characteristic of the suspension spring according to the turning condition of a vehicle.
Such a system has been proposed in Japanese Patent Application Laid-open No. 56-147107 in which the commencement of a vehicle's turning movement is determined from the speed and the angular velocity of the steering wheel, and the damping force of the suspension is changed to have a greater value than normal and then is restored to its standard value in a fixed time interval. While being very advantageous during a short time interval of the turning mode of operation or for a predetermined time interval from the commencement of turning movement, this turning detection system is disadvantageous in that the damping force is restored to the standard value in the course of turning for a long time interval. In a steering operation such as for making a sharp turn along a sharp curve in a road, the steering wheel must be rotated rapidly at the beginning of the sharp turn and remain at a fixed angle during a time interval when the vehicle follows the curve. On the other hand, at the end of the sharp turn when the vehicle tends to go straight, the steering wheel is rotated in a reverse direction with steering wheel angular velocity determined by the curvature of the road and the vehicle speed. Conventional systems such as disclosed in the above Japanese Patent application only consider the vehicle speed at commencement of the turning movement and the steering wheel angular velocity and, accordingly, can not determine a time interval for completion of the turning movement, resulting in the damping force being inaccurately adjusted.